katie davis, nbc news, boston. >>> police officers are searching for evidence. here are people who called in to us to report what they saw. >> we saw smoke, people running hysterically. knocking over the barricades to get off the way. >> you don't know what to do but to ex're get out of there. >> a lot of people on the streets crying. there were a lot of people that obviously saw it. there were a lot of people that didn't, and had no idea what was happening. >> a former army medic said he was inside a building near, and the force of the explosion knocked him to the floor. he got to work treating people until paramedics arrived. >> today's tragedy hit hard, a team from newtown wanted to honor victims of the sandy hook shooting. the runners dedicated each of the 26 miles to the 26 victims. there was a moment of silence, and the newtown seal was placed at the 26 mile mark. all of the runners representing newtown were not injuried in the explosions. >> we are hearing the audio calls. jim henley has more on the chaos and the confusion from the scene today. >> dozens